SNARE-MEDIATED RETROGRADE TRAFFIC FROM THE GOLGI-COMPLEX TO THE ENDOPLASMIC-RETICULUM

Operation of the secretory pathway in eukaryotic cells requires the se lective docking and fusion of transport vesicles with the appropriate target organelle. This is mediated in part by integral membrane protei ns termed v-SNAREs (on vesicles) and t-SNAREs (on the target membranes ). We describe a novel yeast t-SNARE that resides on the endoplasmic r eticulum and mediates retrograde traffic from the Golgi complex. Mutat ion of this protein prevents both the HDEL receptor and a membrane pro tein bearing a dibasic retrieval signal from recycling to the endoplas mic reticulum. Forward traffic is also blocked, but only indirectly. C omparison with other yeast mutants indicates that Sec21p (gamma-COP) a nd Sec20p (an endoplasmic reticulum membrane protein) are also involve d primarily, if not exclusively, in retrograde transport.